SharePoint 2010 Workflows error on SharePoint 2016 Server

Hi @Katerina Michael ,

This “The list of workflow actions on the server references an assembly that does not exist” error usually occurs in case of:

• The Server/PC does not have enough memory,
• ShareCache issue,
• In some cases, This error comes up if the current account doesn’t have local privileges.
• “WSS.Actions” file contains a reference to a custom action.

Solution:
1.The Server/PC does not have enough memory
This error may occur if the system does not have enough memory,

Try to close some programs to free some memory space.
If you are working on VM, you will need to check its memory allocation.
if the memory is less than 6 GB, try to scale it up.

2.Clear SharePoint Designer Cache
Try to clear the SharePoint Designer Cache of the following folders

%USERPROFILE%\AppData\Local\Microsoft\WebsiteCache
%USERPROFILE%\AppData\Roaming\Microsoft\SharePoint Designer\ProxyAssemblyCache
%USERPROFILE%\AppData\Roaming\Microsoft\Web Server Extensions\Cache
Restart the SharePoint Designer

3.The current account doesn’t have local privileges.
If you are working on the Server, try to add the current user to Local Administrator Group.

4.“WSS.Actions” file contains a reference to a custom action.
If the problem still exists that means the Workflow actions has been extended with a custom action that developed in Visual Studio, These custom actions are loaded when your workstation reads the WSS.ACTIONS file on the server.

So to overcome this issue, try to delete “WSS.Actions” file as the following.

Please refer to this blog for more information:
The list of workflow actions on the server references an assembly that does not exist
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